Electron discharge apparatus



April 1940- G. K. TEAL 2,196,278

ELECTRON DISCHARGE APPARATUS I Filed Aug. 31, 1937 DIRECHON 0F MAGNET/6 FIELD r0 UTILIZATION 2 7 l-- c/ncu/r INVENTOR G. K TEAL ATTORNEY Patented Apr. 9, 1940 UNITED- STATES PATENT OFFICE.

Gordon K. Teal, New York, N. Y., assignor to Bell Telephone Laboratories, Incorporated,

New York, N. Y., a corporation of New York Application August 31, 1937, Serial No. 161,748

. Claims.

This invention relates to electron discharge apparatus and more particularly to such apparatus including multistage electron multipliers.

One object of this invention is to expedite the 5 -manifold amplification of electric currents.

Another object of this invention is to improve the efficiency of multistage electron multipliers.

In one illustration embodiment of this invention, an electron multiplier comprises a primary cathode, an anode or collector electrode spaced from the cathode, and a plurality of secondary or auxiliary cathodes between the primary cathode and the collector electrode or anode. The successive secondary or auxiliary cathodes may be operated at progressively increasing positive potentials with respect to the primary cathode so that the electrons emanating from each cathode are attracted to and impinge upon the next following electrode toward the anode orcollector electrode.

In accordance with one feature of this invention, the secondary cathodes are composed of thin metallic sheets or films mounted parallel to one another and in alignment with the primary .625 cathode and the collector electrode or anode.

One or both faces of the metallic sheets or films may be sensitized to render them capable of copious emission of secondary electrons.

In accordance with another feature of this invention, means are provided for concentrating or guiding the electron streams emanating from each of the cathodes so that the streams from each cathode impinge upon the next succeeding cathode or the anode. The concentrating or guiding means may be, for example, a cylindrical coil encompassing the electrodes and producing a strong concentrated magnetic field adjacent and parallel to the axis of alignment thereof. Alternatively, the concentrating or guiding means may 0 include a plurality of coaxial metallic tubular members each of which encompasses a corresponding one of the secondary or auxiliary cathodes and may have a suitable potential applied thereto.

The invention and the foregoing and other features thereof will be understood more clearly and fully from the following detailed description with reference to the accompanying drawing in which:

Fig. l is a view in perspective of an electron multiplier illustrative of oneembodiment of this invention, a portionof the enclosing vessel being broken away to show the electrodes more clearly;

Fig. 2 is a view partly in cross section and partly 5 diagrammatic of electron discharge apparatus including an electron multiplier of the construction illustrated in Fig. l and an electromagnetic coil for concentrating the various electron streams;

Fig. 3 is a View in cross-section of an electron 's multiplier illustrative of another embodiment of this invention, wherein tubular concentrating members are provided for the electron streams,

and I Fig. 4 is a detail view in perspective and partly broken away of one of the cathode-guide structures included in the device shown in Fig. 3.

Referring now to the drawing, the electron discharge apparatus shown in Figs. 1 and 2 comprises an elongated, cylindrical enclosing 'vessel It housing a primary cathode H mounted at one, end of the vessel by a rigid-leading-in conductor I2 and an anode or collector electrode I3 mounted at the opposite end of the vessel Ill and in alignment with the cathode H, by a rigid lead-J ing-in conductor l4. i

As shown clearly in Fig. 2, the primary cathode l I may be a plate disposed at an angle, for exam-. ple', 45 degrees, to the longitudinal axis of the vessel Ill. The inner or lower face of this plate,'- that is, the surface thereof directed toward the anode or collector electrode [3, may be treated to render it photoelectrically active.

Disposed between the primary cathode II and the anode or collector electrode l3 and in align-T30 ment therewith are a plurality of auxiliary or secondary cathodes I5 I5 and I5 Each of these cathodes comprises a rigid, metallic U- shaped frame l6 supported by a leading-in conductor ll sealed in the side wall of the e'nclos- 35 ing vessel Ii] and extending therefrom. Each of the frames [5 carries a thin film or sheet of metal It, the several sheets or films'preferably being parallel to one another and to the anode or collector electrode l3. The-sheets or films I8 may be, for example, of a precious metal such as gold leaf or silver and the faces thereof toward the anode or collector electrode l3 may be sensitized to assure copious emission of secondary electrons therefrom. For example, these surfaces may lee-45 treated with an alkali metal such as caesium, a negative element such as oxygen, and a metal such as silver to produce a matrix or coating containing caesium oxide, silver, and some free caesium.

A suitable screen electrode may be provided adjacent the anode or collector electrode [3 to shield the end secondary cathode I5 from potential variations upon the anode or collector electrode. The screen electrode may comprise a rigid me tallic frame I9 supported by a rigid leading-in conductor 20 sealed in and extending from the side wall of the vessel It], and a mesh portion 2| disposed parallel to the anode or collector electrode I3.

During operation of the device, as shown in Fig. 2, the secondary cathode I may be maintained at a positive potential, for example, of the order of 100 volts, with respect to the primary cathode II, the cathode I5 may be maintained of the order of 100 volts positive with respect to the cathode I5 and, similarly, the cathode I5 may be maintained of the order of 100 volts positive with respect to the cathode I 5 The requisite potentials may be obtained, for example, from a potientometer including suitable resistances 22 in shunt with a source such as a battery 23. The anode or collector electrode I3 and the screen electrode 2| may be maintained at suitable positive potentials, for example, of the order of 300 volts and 150 volts, respectively, with respect to the final secondary electrode by sources such as batteries 24. An output or utilization circuit may be connected between the cathode II and anode or collector electrode I3 as shown.

The primary cathode il may be energized or activated to produce a stream of electrons, as by a light beam emanating from a source 25 and focussed upon the photoelectrically active surface of the cathode Ii by a suitable lens, not shown. The intensity of the light beam, and hence the intensity of the electron stream emitted from the cathode II may be varied in accordance with the 4 impulses to be translated or amplified, by a sound Under the influence of the potential upon the secondary or auxiliary cathode it), the electrons emitted by the primary cathode 1'! flow with relatively high velocities toward the film I8 of the cathode I5 and impinge upon the surface thereof facing the cathode El. As a result of this impingement of electrons, secondary electrons are released from the surface of the film E8 of the cathode I5 facirr the next secondary or auxiliary cathode I5 It has been found that the secondary electron current emanating from the cathode I5 is many times greater than the impinging primary electron current. Consequently, in effect an electron multiplication and hence an amplification of the primary current is obtained.

The secondary electrons released from the cathode IE3 travel at fairly high velocities toward the cathode I5 and impinge upon the film I8 thereof as a result of which other secondary electrons are released and an electron multiplication occurs. Similarly, the secondary electrons released from the film l8 of the cathode I55 flow to the next succeeding cathode l 5 and still other secondary electrons are produced and further multiplication occurs. The secondary electrons released from the cathode I5 flow to the anode or collector electrode 83 and constitute the output current of the apparatus which is greater than the current emitted by the primary cathode II.

In order to prevent dispersion of the electron streams flowing between the cathodes and ther by to insure the impingement of substantially all of the electrons emitted from the surfaces of the cathodes toward the anode or collector electrode, upon the next succeeding cathode or the anode, means are provided for concentrating or focussing the several electron streams. As shown in Fig. 2, this concentrating or focussing means may include an elongated coil 21 encompassing the enclosing vessel Ill and mounted coaxial with the electrodes therein. The coil 21 is energized in a suitable manner to provide a strong concentrated magnetic field along the axis of alignment of the electrodes, the field having the direction indicated in Fig. 2.

In the embodiment of this invention illustrated in Fig. 3, the several sheets or films I8, of the secondary cathodes suitably sensitized as described heretofore, may be circular and, as shown more clearly in Fig. 4, may be carried by rigid metallic rings or frames 28. Each of the rings or frames 28 is afiixed within a tubular metallic sleeve 29, preferably midway between the ends of the sleeve. The several sleeves 29 preferably are of the same diameter and are mounted coaxially with one another by rigid leading-in conductors 3tsealed in and extending from the side wall of the enclosing vessel ID. The various electrodes may be connected in the same manner as illustrated in Fig. 2.

Each of the tubular sleeves 29 is at the same potential as the corresponding film I8 carried thereby and serves, both mechanically and electrically, to minimize dispersion of the electron streams emanating from the cathodes so that the electrons from each cathode are concentrated and are focussed upon the next succeeding cathode or upon the anode or collector electrode.

Although specific embodiments of the invention have been shown and described, it will be understood, of course, that various modifications may be made therein. For example, although three secondary or auxiliary cathodes have been indicated in the specific embodiments shown and described, a greater or lesser number may be employed. Also, although the primary cathodes I l have been illustrated as of the photoelectric type, they may be of the thermionic type, directly thereadjacent to vary the intensity of the primary electron stream. Likewise, although the concentrating sleeves 29 have been shown as cylindrical in form, they may be of other forms, for example, frusto-conical and tapered toward the next succeeding electrode. Other modifications may appear to those skilled in the art without, however, departing from the scope and spirit of this invention as defined in the appended claims.

What is claimed is:

1. Electron discharge apparatus comprising a primary cathode, a collector electrode, a plurality of imperforate parallel secondary cathodes mounted one behind another and between said primary cathode and said collector electrode, each of said secondary cathodes having the surface thereof toward said collector electrode sensitized to emit secondary electrons, and means electrically integral with and encompassing said secondary cathodes for concentrating the electrons emitted from each of said secondary cathodes.

2. Electron discharge apparatus comprising a primary cathode, a collector electrode, a secondary electron emitting cathode between said primary cathode and said collector electrode, and a tubular metallic member supporting and encompassing said secondary cathode, and mounted in alignment with said primary cathode and said collector electrode, said secondary cathode being mounted intermediate the ends of said tubular member.

3. An electron multiplier comprising a primary cathode, a collector electrode, a plurality of or indirectly heated, and a grid may be provided secondary cathodes mounted one behind another;

between said primary cathode and said collector electrode, and a plurality of coaxial tubular members each encompassing a corresponding one of said secondary cathodes, each of said secondary cathodes being mounted remote from both ends of the corresponding one of said tubular members.

4. An electron multiplier comprising a primary cathode, a collector electrode in alignment with said primary cathode, a plurality of spaced coaxial tubular members between said primary cathode and said collector electrode, and a secondary electron emitting cathode within each of said tubular members and carried thereby, each secondary cathode being mounted substantially mid-way between the ends of the tubular member by which it is carried.

5. An electron multiplier comprising a primary cathode, a collector electrode in alignment with said primary cathode, a plurality of metallic tubular members between said primary cathode and said collector electrode. said members being coaxial and mounted end to end in alignment with said primary cathode and said collector electrode, and a plurality of metallic film electrodes each mounted within a corresponding one of said GORDON Kl TEAL. 

